1. Field of the Invention
This invention relates generally to a Radio Frequency Identification (RFID) system. More particularly, it relates to an adaptive antenna array for a RF reader for increasing the operating range of the RFID system.
2. Description of Related Art
A conventional Radio Frequency Identification (RFID) system consists of a reader and a plurality of RF tags. The RF reader transmits a radio signal containing a unique identification (ID) to poll one of a plurality of RF tags. The RF tag polled responds by sending back a radio signal. A variety of RFID systems have been used in different applications such as warehouse inventory control systems.
There are two types of conventional RFID systems: active and passive. The RF tag in the active RFID system requires power to operate. For the battery-powered active RF tag, it is desirable to have reduced power consumption so that the operating life can be extended. The RF tag in the passive RFID system derives and stores power from a RF signal transmitted by the RF reader and responds by transmitting back a signal by using the stored energy. Conventional RFID systems are limited to short range operation because of limited transmission power available on the return link from the RF tag to the RF reader. RFID systems typically contain a small number of RF readers and a large number of RF tags. The RF tags typically have limited complexity and low cost. Accordingly, the majority of the complex signal processing and the associated implementation are at the RF reader side. It is desirable to increase the operating range of the RFID system.